[6.0] Missions To Mars (1)

v2.0.0 / chapter 6 of 20 / 01 jul 16 / greg goebel

* Early astronomical observations of Mars suggested a desert planet, but one that appeared to have widespread vegetation, or even evidence of huge artificial structures. Beginning in the mid-1960s, space probes revealed that our knowledge of Mars was very incomplete and largely incorrect, leading to completely revised views of the Red Planet.

classical map of Mars



* The planet Mars is the fourth planet from the Sun in the solar system. It is one of the five planets clearly visible to the naked eye and so known to the ancients. The Romans gave it the name Mars after their god of war, for its red color.

Before the beginning of the space age, some simple facts were known about Mars. It orbits the Sun at about 1.5 times the distance of Earth, or about 228 million kilometers, in an orbit that lasts almost exactly 687 Earth days. It has a diameter a little more than half that of the Earth, or 6,787 kilometers; a little over a tenth the Earth's mass; a surface gravity about 0.38 that of the Earth's; and a day that lasts 1.03 Earth days. The Red Planet's axis of rotation is tilted 24 degrees to the plane of its orbit around the Sun, very close to the Earth's axial tilt of 23 degrees.

Mars has two tiny and irregularly-shaped moons, named "Phobos (Fear)" and "Deimos (Terror)" after the servants of the god Mars. Phobos is the inner moon, orbiting the planet at an altitude of 9,400 kilometers, with a period of 0.319 Earth days, and dimensions ranging from 27 to 19 kilometers. Deimos is the outer moon, orbiting the planet at an altitude of 23,500 kilometers, with a period of 1.263 Earth days, and is even smaller, with dimensions ranging from about 15 to 11 kilometers. The orbits of both moons are very circular, and essentially in the same plane as the Martian equator.

Aside from these facts, not much was honestly known about Mars before spaceflight, and much of what was believed was simply wrong -- a demonstration of how science amounts to nothing much better than the data on which it is based.



* Although the motion of Mars had been plotted with increasing care since the time of the ancient Greeks, it wasn't until the early 17th century, with the invention of the telescope and the increasingly widespread realization that the planets were worlds of their own, that astronomers began to observe Mars to see what kind of place it really was. Early telescopes did not reveal much about the planet; of course, the tiny moons were invisible and would remain so for the better part of two centuries.

Once every 26 months, Mars and Earth perform an "opposition", where their paths in their orbits bring them to a minimum distance; such oppositions are a prime opportunity to obtain better observations of Mars. One of the first recorded sketches of the Red Planet was made by an Italian amateur astronomer, Francisco Fontana, during an opposition in 1638 -- but Fontana's sketch provided no details that weren't later shown to be due to defects in his telescope. The first sketch of Mars to show details that we now know to be valid was made by the Dutch astronomer and polymath Christiaan Huygens in 1659. Huygens was a meticulous observer, and his sketch, though crude, does show what is now known as the "Syrtis Major" region of the planet.

A rival of Huygens, the French astronomer Jean-Dominique Cassini, born in Italy as Giovanni Domenico Cassini and director of the Paris observatory, determined in 1666 a reasonable value of 24 hours 40 minutes for the Martian day, which is only 2.5 minutes longer than the actual value. Cassini was also the first to notice that Mars had white polar icecaps, which were soon observed to grow and shrink with the passing of Martian seasons, and would later be observed to be offset from the planet's poles of rotation.

* The next major figure in the early days of Mars exploration was Sir William Herschel, mentioned in previous chapters, one of the towering figures of astronomy. Sir William Herschel was born on 15 November 1738 in the German state of Hanover as Friederich Wilhelm Herschel. He received a musical education and became skilled in both performance and composition before he emigrated to England in 1757. There, after a time as a freelancer, he obtained a permanent position as a church organist and choir director. Having achieved financial security, Herschel began to extend his interests, tinkering with math, optics, and finally astronomy. He was dissatisfied with the refracting telescopes of the time and built his own reflecting telescopes that proved far superior. Herschel not only owned the best equipment of the era, he was also one of the most outstanding astronomical observers of history. He was meticulous, seemingly tireless, and recorded his observations in great detail and accuracy.

Among his many observations were studies of Mars during oppositions between 1777 and 1783. Herschel examined the icecaps closely, and provided estimates of the planet's diameter and axial tilt. He also observed "stellar occultations" by Mars, where the planet passed in front of the stars, and concluded correctly that since the light of the stars winked out abruptly that the atmosphere of Mars was thin at best. However, it did appear to have some atmosphere, as rapid changes in the planet's appearance implied the action of clouds or other atmospheric phenomena. Much later, such major changes would be linked to huge Martian dust storms.

Herschel's studies of Mars were followed up by three German astronomers, Johann Hieronymous Schroeter, Wilhelm Beer, and Johann von Maedler. Schroeter was a dedicated planet-watcher and produced a series of sketches of Mars until 1814, when his observatory was sacked during the Napoleonic Wars. He died, broken-hearted, in 1816. Beer and von Maedler, mentioned in a previous chapter for their detailed map of the Moon, also constructed the first map of Mars, which was reasonably accurate given the tools available to them.

* Observations continued through the mid-19th century, resulting in improved maps. With the maps came the issue of naming Martian surface features. Through the telescope, Mars is a red world broken up by dark patches and the polar icecaps. It was plausible at the time to think that the dark patches were oceans of some sort, or regions of vegetation, and such concepts guided the assignment of names. The first naming scheme was proposed by Paul Proctor, a British amateur astronomer and popular science writer, in 1867. However, his map was regarded as inaccurate, and his naming scheme was criticized because it favored the names of Britons -- which hardly seemed fair since the British had no special claim on Mars observations.

A more enduring scheme was devised by an Italian astronomer named Giovanni Schiaparelli, director of the Milan observatory. In 1877, Schiaparelli performed detailed observations of the Red Planet during the opposition of that year, and used the observations to construct the best map of the planet to that time. This map used names that is still in use today -- though with inaccurate descriptive designations, such as "Mare" for nonexistent "seas", later replaced by more accurate designations, such as "Planitia" for "plains".

* 1877 was also significant in that it was the year of the discovery of the two Martian moons, Phobos and Deimos. They were discovered by an American astronomer, Asaph Hall, who was performing observations with a 66-centimeter refracting telescope in Washington DC. He was deliberately looking for Martian moons, and caught a glimpse of what might be a moon on 10 August.

Any Martian moon had to be tiny to have missed being spotted by that time, and certainly Hall's expectations might have led him to grasp at straws, but he was a careful and methodical observer. Poor weather hindered his observations for the next few nights, but on 16 August, Hall not only spotted his moon again, but the next night also found a second moon. He continued his observations for the next several nights to make sure, and concluded that the inner moon actually orbited Mars in a third of a Martian day. No other moon had ever been seen to orbit a planet faster than the planet rotates, but after repeated observations he was forced to conclude that this one did. Hall had the clear honor of naming the moons, and he selected "Phobos" and "Deimos" on the basis of a suggestion by a "Mr. Madan of Eton, England".

Oddly, the discovery of the two moons had been foreshadowed in 1727 by the English satirist Jonathan Swift in one of the installments of his classic novel GULLIVER'S TRAVELS, titled VOYAGE TO LAPUTA. In this story, the wise men of the kingdom of Laputa discovered "two lesser stars, or satellites, which revolve about Mars, whereof the innermost is distant from the center of the planet exactly three of his diameters, the outermost five; the former revolves in the space of ten hours, the latter in twenty-one and a half."

That was remarkably close for a outright guess, but not close enough to suggest that Swift had supernatural insight. The French satirist Voltaire also mentioned two Martian moons in his book MICROMEGAS, but on being questioned on why he had selected two moons, he replied simply that as Earth had one moon, it was logical that Mars, the next planet in the solar system, had two. Voltaire was likely making a small joke of sorts, but people sometimes do buy into such arguments.



* The discovery of Phobos and Deimos was a triumph for Hall, but it was Schiaparelli's 1877 map that would preoccupy astronomers for the better part of a century. The map included a set of features that Schiaparelli called "canali" or "canals", and he later wrote of them:


All the vast extent of the continents is furrowed upon every side by a network of numerous lines or fine stripes of a more or less pronounced dark colour, whose aspect is very variable. They traverse the planet for long distances in regular lines, that do not at all resemble the winding courses of our streams. Some of the shorter ones do not reach three hundred miles; others extend for many thousands, occupying a quarter or even a third of the circumference of the planet ... The canals may intersect among themselves at all possible angles, but by preference they converge towards the small spots to which we have given the name of lakes.


Schiaparelli documented about 40 canals during his 1877 observations. The astounding thing was that they seemed to follow an orderly pattern, following "great circle" routes or smooth arcs over the surface of the planet. They always seemed to link a dark area with a dark area. Schiaparelli refined his map during the opposition of 1879, adding more canals and noticing that some of them seemed to be "twins", with two parallel channels. Other astronomers had noticed such canals before Schiaparelli, but had not made much of them. Schiaparelli emphasized them -- though many other astronomers claimed they couldn't see them, or if they did see them, they didn't get the same pattern of lines.

The following oppositions of Mars were not as favorable as those of 1877 and 1879, and so there remained room for reasonable doubt. Then, in 1886, two French observers, Perrotin and Thollon, used a powerful 76-centimeter telescope sited at Nice to make an improved map that enthusiastically displayed the canals. There was less objection to the idea after that, with those failing to see them keeping their doubts more or less to themselves. Even those who did see them admitted they were faint, and so those who didn't could well believe their was some limitation in eyesight, equipment, or viewing conditions that kept the canals invisible.

* Another prominent astronomer, William H. Pickering of Harvard University in the US, had a formidable reputation as an observer, and in the 1890s he performed observations of Mars that were regarded as authoritative. He gave the name of "oases" to the dark junction points between the canals, and also observed canals crossing the dark areas of the planet, undermining the notion that the dark areas were "seas".

Pickering's work was overshadowed by that of another American, Percival Lowell. Lowell was born in 1855 to an aristocratic Boston family. He achieved substantial wealth in his family's businesses and had a minor career in international diplomacy. However, he had been trained as a mathematician, having graduated from Harvard with honors in the subject, and had a keen interest in astronomy. In 1893, Lowell established his own astronomical observatory in the mountains outside Flagstaff, Arizona. The location was excellent; he equipped it with first-class instruments, particularly a 61-centimeter refracting telescope; and he hired a professional staff to help him. Lowell spent much of his time observing Mars.

Lowell was a true believer in the canals, often writing articles about them. In 1906, he published a book titled MARS AND ITS CANALS that discussed his ideas about them. He thought they were clearly artificial, a network of waterways constructed by an ancient and enlightened Martian civilization to funnel water from the polar icecaps to the dry desert regions of the equator. Lowell also claimed to see a "wave of darkening" down from the polar areas in the Martian spring, as if water was reviving vegetation that had gone dormant for the winter.

Lowell's ideas were appealing and popular. The English writer Herbert George Wells leveraged off them in his 1898 novel THE WAR OF THE WORLDS, in which the advanced Martians proved to be somewhat less enlightened than Lowell suggested, leaving their dying planet to invade Earth and smash the predominant human societies, much as those societies had seized colonies in Asia and Africa. Lowell's notions of Mars also later influenced Edgar Rice Burroughs, who wrote a series of novels about "John Carter of Mars" and his swashbuckling adventures on the Red Planet, known to its inhabitants as "Barsoom".

* It must be emphasized that though Lowell's ideas were the basis for sensationalistic novels, he was no crank. To be sure, Lowell's vision of a great Martian civilization turned out to be a fantasy, but at the time there was nothing in his ideas that flew in the face of the facts. The worst that could be said of him was that his imagination ran away with him, but it was such a marvelous imagination that it is hard not to find it seductive even now.

Not everyone shared Lowell's enthusiasm. No two observers agreed completely on the configuration of the canal network, and the well-known American astronomer George Ellery Hale flatly said he couldn't see the canals at all. Asaph Hall said he couldn't see them, either. There was certainly no hint of them in photographs of the planet, and it seems odd that more was not made of that fact. Some believed the canals were the power of suggestion at work, with the eye and brain assembling strings of features on the Martian surface into linear canals -- a suggestion that infuriated Lowell. There was a similar controversy over the "wave of darkening".



* The controversy over the canals continued for almost half a century after Percival Lowell. The idea that the canals were elements of an artificial network was largely rejected, but the argument went on over the existence of the canals, and even in the late 1950s maps of Mars were published that displayed them.

Observations continued, with astronomers coming up with rough estimates of the density of the Martian atmosphere by trying to gauge the atmospheric attenuation of light at the center of the planetary disk as compared to the edges. The estimates tended to cluster around a value of about a tenth of the Earth's sea-level atmospheric pressure.

Spectroscopic analysis of the chemical composition of the Martian atmosphere had been performed since the invention of astronomical spectroscopy in the 1860s, but this procedure was tricky, since the only source of light for spectroscopic analysis was sunlight reflected off the Martian surface. The reflected light was very faint and subject to various confounding influences. Astronomers claimed to detect water vapor and carbon dioxide, but no oxygen. The bulk of the atmosphere was presumed to be nitrogen, which is the major constituent of the Earth's atmosphere, and is hard to detect by spectroscopic means. Mars observers remained uncertain as to the nature of the polar icecaps. While they had long been assumed to be made of water ice, Percival Lowell had constructed an argument to suggest that they were made of "dry ice", or frozen carbon dioxide.

Observers occasionally saw huge dust storms raging over the planet, sometimes covering the entire Martian surface. Major dust storms were observed during oppositions in 1909, 1924, 1941, 1956, and 1971:1972. The dust storm of 1909 was particularly intense. Dust storms seem to occur when Mars is at the "perihelion" of its orbit, or closest approach to the Sun.

* In short, despite the fact that astronomers had been watching Mars for centuries, they still knew remarkably little about it. However, by the late 1950s, spaceflight technology was opening new doors for planetary astronomers. Instead of peering at Mars through telescopes, spacecraft would soon be able to fly to the planet to inspect it directly.

In fact, enthusiasm for spaceflight in the late 1950s and through most of the 1960s was so great that some astronomers thought they might live to visit Mars personally. This was the great age of the space race; space was an open frontier, and exploration would expand rapidly, with ever more spectacular expeditions to other worlds. The Moon seemed in reach, and the next step was Mars, which in turn would be a step to the other planets.

In the mid-1950s, the American COLLIERS magazine featured a series of articles on the exploration of space by prominent spaceflight researchers such as Dr. Wernher von Braun. The articles attracted a great deal of public attention, partly because they featured beautiful paintings by the artist Chesley Bonestell. Bonestell's illustrations included domed Mars bases and great winged spacecraft, designed by von Braun, sailing through the Martian sky.

Von Braun's Mars expedition

In April 1959, only six months after NASA had been pieced together out of a set of different government aerospace agencies, engineers from the NASA Lewis Research Center in Ohio went to the Senate Committee on Aeronautical & Space Sciences to beg funding for a study on a crewed Mars expedition.

NASA Lewis had in fact been considering propulsion technologies that would be applicable to a crewed Mars mission since 1957. High on their list of candidates were "nuclear thermal rocket (NTR)" engines, in which hydrogen is heated to high temperature by being pumped through a nuclear reactor core and then shot out an exhaust; and "electrostatic ion rocket (EIR)" engines, in which a relatively heavy element such as cesium is ionized and then accelerated to high exhaust velocities using high-voltage grids. Congress authorized funding for the study, and the NASA Lewis group duly published their report in January 1960.

The report envisioned the launch of a Mars "cruiser" fitted with an NTR engine into Earth orbit, where the engine core was activated. At the appropriate time, the cruiser used its engine to boost itself into a Mars trajectory; and months later, on arrival at Mars, the cruiser used its engine to put itself into orbit around the planet. Explorers then descended to the planet's surface using a landing craft, where they conducted exploration for an extended period of time.

When the "launch window' for the return trip to Earth opened, the astronauts returned to the cruiser in the landing craft. The cruiser then boosted out of Mars orbit to cruise back to Earth. On arrival at Earth, the cruiser went into a parking orbit, and the crew returned to the ground in a reentry capsule. This scenario remained the baseline concept for Mars exploration for decades.

* A comparable, if more ambitious, concept was developed at about the same time by Ernst Stuhlinger, a civilian employee of the US Army Ballistic Missile Agency (ABMA) at Redstone Arsenal, in Huntsville, Alabama. His boss at ABMA was von Braun, who had led the World War II German effort to develop the V-2 ballistic missile at the island of Peenemunde in the Baltic. Stuhlinger had also worked for von Braun at Peenemunde, and when the war ended, von Braun, Stuhlinger, and many of the other engineers at Peenemunde were recruited by the US Army to build missiles for America, instead of the Nazis.

Stuhlinger envisioned a Mars exploration fleet of five cruisers, propelled by nuclear-powered EIR engines. In his concept, the engines were mounted in a central node, with a long truss running through the node. Crew quarters were at one end of the truss, and the nuclear reactor was at the other. The truss spun around the central node to provide artificial gravity for the crew. The nuclear reactor drove a turbine to generate electricity for the EIR engine and to power the cruiser's other systems. The truss was surrounded by a large radiator surface to provide cooling for the turbine working fluid.

Stuhlinger's Mars fleet achieved some notoriety when the popular TV show WALT DISNEY'S WONDERFUL WORLD OF COLOR broadcast an episode titled "Mars & Beyond", featuring Stuhlinger's Mars craft. This was part of a series of episodes promoting spaceflight at least partly orchestrated by von Braun, an exercise that later led some wits to observe that von Braun and Stuhlinger were among the few people to have ever worked for both Adolf Hitler and Walt Disney.

* On 25 May 1961, American President John F. Kennedy announced in a speech the intent of the United States to put a man on the Moon by the end of the decade. NASA now focused its energies on the Moon project, with other efforts taking second place.

By that time, part of ABMA had been spun off to become NASA's Marshall Space Flight Center. Von Braun knew that once his big Saturn Moon rockets were complete, Marshall might find itself out of a job, and he wanted to find something to carry the organization after Saturn.

In mid-1962, Marshall initiated studies under the title of "Early Manned Planetary Interplanetary Roundtrip Expeditions (EMPIRE)", which focused on relatively modest Mars expeditions that could be implemented in the post-Apollo timeframe. It seems a little hard to believe that nobody noticed that the name EMPIRE might imply "bureaucratic empire building", but these were less cynical times. Of course the used of the term "manned" was characteristic of the times, when NASA had no strong inclination to put women into space. The emphasis was on Mars flyby and orbiter missions, not Mars landing missions. Lockheed, Ford Aeronutronic, and General Dynamics performed studies.

The General Dynamics study was performed by Krafft Ehricke, a German tank commander and Peenemunde graduate who had helped General Dynamics develop the Atlas intercontinental ballistic missile. Ehricke was an imaginative fellow whose clever concepts were often featured in popular space literature of the time, and were even realized as plastic model kits. His concept for using an Atlas booster as a space station led indirectly to the US Skylab space station.

Ehricke designed a fleet of Mars spacecraft using NTR propulsion, with the fleet including both cargo and crew vessels. The astronauts would travel between spacecraft in the fleet on "space taxis", and take refuge in one of the cargo vessels if a crew vessel failed. The crew vessels tumbled to provide artificial gravity. As with most of Ehricke's other proposals, he described the EMPIRE technology in great detail. He cheated on the specifications for the design effort, however, with his spacecraft to support both orbital and landing missions. The Lockheed and Ford Aeronutronic were more conservative, though they used similar technology.

* By 1963, other NASA centers were getting into the Mars act. The NASA Manned Spaceflight Center (MSC) in Houston, which later became the Johnson Spaceflight Center, conducted Mars studies under the direction of Assistant Director of Engineering Max Faget. Faget had no high opinion of the concept of the crewed planetary flyby mission, stating in 1962: "The flyby mission will demand the least energy, but will also have the least scientific value." Faget wanted to build up a space infrastructure, with a space station and a Moon base leading to planetary exploration. Faget believed that robot probes were better suited to the flyby mission.

However, the Houston MSC did conduct an in-house Mars mission study that combined flyby trajectories with a landing mission. The idea was for a first flyby spacecraft to drop off a crewed lander, which would conduct explorations of the surface of the planet, and then lift off again to rendezvous with a second flyby spacecraft. The idea was interesting, but in hindsight clearly left an unacceptably small margin for error.

Houston MSC also worked with Ford Aeronutronic to design a Mars lander, which was a flatiron-shaped lifting body. The lifting body assumed, following the beliefs of astronomers of the time, that Mars had an atmosphere composed mostly of nitrogen, and had a density a tenth that of the Earth's atmosphere. The lander scenario envisioned the astronauts searching for Martian life, and even studying it to see if it were edible, an idea that suggests plots for really cheesy horror movies.



* While some NASA centers were conducting elaborate studies for crewed missions to Mars, NASA's Jet Propulsion Laboratory was working on their much more modest Mariner probes, and in fact managed to perform the first successful interplanetary mission, with Mariner 2 flying by Venus in 1962.

Mars and Earth are properly aligned for an interplanetary trajectory once every 26 months. A Mars launch window opened in November 1964, and the next two Mariners, "Mariner 3" and "Mariner 4", were sent to Mars. These were identical flyby probes, each weighing about 260 kilograms, and launched by Atlas Agena boosters. They were improved versions of the Mariner 2 probe, with four solar panels arranged in an "X" rather than two and a more sophisticated instrument payload, including:

All NASA Mars flyby and orbiter probes up to the 1990s had the same basic configuration -- just increasingly scaled up in size, with improved instruments and other systems.

Mariner 4 on the pad

Mariner 3 was launched on 5 November 1964, but never made it out of Earth orbit because the Agena's payload shroud failed to open. Mariner 4 was launched on 28 November 1964 and flew past Mars with a closest approach of 9,846 kilometers on 14 July 1965, returning 21 low-resolution photographs covering a very small portion of the Martian surface. As it completed its flyby, it passed behind Mars, with mission scientists using the occultation of the spacecraft's radio signal to determine the density of the Martian atmosphere.

Incidentally, although the images were produced by facsimile, dealing with the data was very time-consuming given the primitive hardware of the time, and the mission staff cooked up one image by printing out the numeric values returned by the camera and then drawing them up appropriately using a set of "pastels" -- crayons, more or less.

Despite the crudity of the probe, Mariner 4's visit was still the biggest leap in knowledge about Mars in the entire history of the exploration of the planet to that time. Instead of showing a planet with canals and oases, it showed a cratered, barren world that looked like the Earth's Moon. The radio science occultation experiment showed that Martian atmospheric density was only a hundredth that of the Earth's, and it was mostly carbon dioxide. Earth-based astronomers had been wildly off in their analysis of the planet. By all evidence, Mars was a thoroughly dead world.

* However, Mariner 4 really only provided a few tantalizing snapshots of the Martian surface. It was followed by two more Mars flyby probes, "Mariners 6" and "Mariner 7". (Mariner 5, which was similar to Mariner 4, was a Venus probe, mentioned in the previous chapter.) The basic configuration of these two probes was similar to that of Mariners 3 and 4, but Mariners 6 and 7 were larger, weighing 420 kilograms each, and they had a more sophisticated instrument suite carried on a scan platform on the bottom of the spacecraft bus. Each probe carried;

Mariner 6 was launched by an Atlas Centaur booster on 24 February 1969, followed by Mariner 7 on 27 March 1969. Mariner 6 flew by Mars on 31 July 1969, followed by Mariner 7 flew by on 4 August 1969. Closest approach of both probes was about 3,550 kilometers. They returned 143 "approach" images and 55 close-up images, including a small, coarse image of Phobos.

* The close-ups of Mariner 6 and 7 again revealed a cratered world, reinforcing the impression that Mars was much more like the Moon than Earth. This impression was misleading, as was proven by the next NASA Mars mission, "Mariner 9", which was the first successful planetary orbiter and provided the first really detailed map of Mars.

Mariner 9 was launched along with "Mariner 8" in 1971. They had the same basic configuration as earlier Mars Mariners, but were substantially bigger, at about 974 kilograms. The instrument suite was similar to that of Mariner 6 and 7, but included two cameras -- a wide-angle camera and a close-up camera -- instead of one. They were also launched by Atlas Centaur boosters.

Mariner 9

Mariner 8 was launched on 8 May 1971, but never made Earth orbit due to the failure of the Centaur upper stage. Mariner 9 was launched on 30 May 1971, and went into Mars orbit on 13 November 1971. It arrived while a planet-wide Martian dust storm was in progress -- which had been expected, since Mars was near perihelion at the time.

After the dust settled down, Mariner 9 got down to business, returning 7,329 images over the total of 349 days it operated before being finally shut down. The images included the first close-ups of Phobos and Deimos. On full inspection, Mars was not as moonlike as the Mariner flybys had suggested. The images revealed huge volcanoes, a 4,000-kilometer-long grand canyon, and river-like channels. Mars began to seem interesting again.



* While the Americans launched their Mariner Mars probes, the Soviets launched a series of their own Mars probes, but with far less success. The Soviets had actually been the first to attempt to send probes to Mars. They tried to launch "Mars 1M" flyby probes on Molniya boosters on 10 October and 14 October 1960, but neither made orbit. Description of these spacecraft remains unclear.

They tried again in 1962, launching "Mars 2MV" flyby probes on 24 October, 1 November, and 4 November. Description of these probes is also unclear; at least one of them may have carried a hard-lander capsule. The first of the three broke up in Earth orbit, with the debris designated "Sputnik 22". The Cuban Missile Crisis was in progress at the time; the debris caused some short-lived alarm in the US defense network, since it looked like it might be a missile.

The second actually made it into interplanetary space, being designated "Mars 1", but contact was lost on 21 March 1963, apparently because it broke star-tracker lock and could no longer point its communications antenna back to Earth. It passed by Mars at a distance of a few hundred thousand kilometers in mid-June, but no data was returned. The third made it into orbit but got no further, being designated "Sputnik 24".

The Soviets launched "Zond 2" on 30 November 1964 to race to the Red Planet against NASA's Mariner 4. It was a Mars 3MV spacecraft, similar to the Venera 3MV series. However, as with Mars 1, contact was lost in mid-flight, communications with the spacecraft ending in April 1965. The USSR did not perform any Mars flights during the 1967 launch window.

The Soviets launched two Mars probes during the 1969 launch window to compete with NASA's Mariner 6 and 7. They were "Mars M-69" orbiter-landers, heavy spacecraft launched by Proton boosters, with the landers having the same general configuration as the Luna E-6 landers. The first of the two probes was launched on 27 March and the second on 2 April. Neither made orbit. The first suffered an upper stage failure. The second flipped sideways just as it rose off the launch pad, traveled a short distance, and then blew up in a tremendous explosion that spewed its toxic propellants all over the area, preventing any other launch attempt until the Mars window was closed. The Proton would be used for all following Soviet Mars shots, generally proving much less erratic in its operation once the bugs were worked out.

The Soviets launched three more Mars probes in the 1971 launch window in competition with Mariner 9. These spacecraft were "Mars M-71" spacecraft, improved versions of the Mars M-69 with both orbiter and lander probe:

The two orbiters did manage to return data for several months. Although their imagery was basically useless because of the dust storm in progress, they were able to use other instruments to obtain useful information on Martian surface and atmospheric conditions.

The Soviets were particularly ambitious during the 1973 launch window, sending a total of four probes to Mars. They were all "Mars M-73" probes, enhancements in turn of the Mars M-71 probes. The first two were orbiters only, while the second two were configured as flyby probes with a lander system.

As it turned out, all four spacecraft had been subjected to a preflight test that involved use of a helium atmosphere. The helium contaminated the integrated circuitry and led to a series of electronics failures during the flight to Mars. These humiliating setbacks were painful, particularly since the USSR had been very successful in Venus exploration. Reporter Donald Neff of TIME magazine invented a beast named the "Great Galactic Ghoul" to account for the troubles encountered by American spacecraft; given the sad record of Soviet Mars exploration, it appeared that the Ghoul was strongly anti-Communist. The Soviets gave up on Mars exploration until the late 1980s. They had not seen the last of the Ghoul.



* The Mariner probes drastically changed thinking about Mars and Mars exploration. If the Mariners had actually seen canals or evidence of a Martian civilization, the pressure for a crewed mission to the Red Planet would have been irresistible -- but the cratered world revealed in the Mariner images didn't excite the imagination of the general public. The fact that a robot probe had obtained such revelations also confirmed Max Faget's opinion that crewed flyby missions were a dead end. However, that didn't prevent NASA from still giving crewed missions a bit of thought. In 1966, Charles Townes, a Nobel laureate and in charge of the NASA Advisory Council, suggested investigating the idea again.

The result was a study that envisioned a crewed flyby probe that sent a robot lander ahead to the planet. The lander would obtain a sample and then blast off again and rendezvous with the flyby probe. This would allow the crew of the flyby spacecraft to analyze the sample immediately, permitting them to identify Martian lifeforms that would probably not survive an interplanetary flight back to Earth.

By 1967, however, the brash New Frontier mentality of the early 1960s was bogging down in domestic unrest and the war in Vietnam. Public enthusiasm for space spectaculars was fading and budget deficits were deepening. Although NASA officials had been told by their political masters that major new space initiatives were out of the question, some of the Mars planners didn't get the message, and put out a request for bids on design of the Mars sample return probe for the crewed flyby mission. Congress quickly killed the request, and also shot down a robot Mars lander named "Voyager".

* NASA's major reason-to-be during the 1960s was the Apollo Moon program. Whatever doubts there may be now about Apollo, it was without argument a great success in terms of achieving its stated goals, and was arguably the high point of NASA's history. Much of the credit for making the Apollo program work must go to NASA Administrator James Webb, a tough, pragmatic, and shrewd government technocrat. Webb helped push Apollo through by focusing on the mission and ensuring that NASA's plans for the post-Apollo timeframe were kept on a low profile.

Webb left the post in 1969 and was replaced by Tom Paine. Paine was much less politically astute than Webb, and had big-time schemes for space exploration that were completely contrary to the changed attitudes of the time. George Mueller's Office of Manned Space Flight came up with a grand plan for a space station, a Moon base, and a Mars flight by 1982. The Mars expedition envisioned two huge nuclear-powered spacecraft that would have cost tens of billions in contemporary dollars. NASA received cautious encouragement for their grand plans, but then reality intervened, in the form of the space shuttle. By 1971 NASA, scrambling to find funds in a chilly political environment to develop the shuttle, canceled all work on crewed Mars missions. NASA veterans recollect that even mentioning a crewed Mars mission was asking for trouble with the management.

* Fortunately, NASA did plan one more set of robot missions to Mars in the 1970s. The Voyager Mars lander project was resurrected in the form of the "Viking" project, resulting in two space probes that arrived at Mars in 1976, with each probe consisting of an orbiter and a lander. The Voyager name was recycled for a pair of outer-planet flyby probes that proved extremely successful and are discussed later.

Viking orbiter

The Viking orbiters weighed 2,320 kilograms each, fully fueled. They resembled scaled-up versions of the Mariner probes and were launched by big Titan III boosters. The orbiters featured a moveable scan platform carrying:

Their communications systems were also used to conduct radio science experiments.

The landers were descendants of the Surveyor Moon lander spacecraft. The Viking Mars landers weighed 576 kilograms each, were each dropped into the Martian atmosphere in an "aeroshell", which absorbed the heat of friction. A parachute system was then deployed and the aeroshell was discarded. The lander floated down on the parachute until it reached low altitude, and then fell to the Martian surface using retrorockets, landing on its three legs.

Each lander was powered by two RTGs, with thermal radiator systems specially designed to work in a planetary atmosphere instead of space. The lander instrument suite consisted of:

The lander communications system supported direct communications with Earth, and so the orbiters were not used as radio relays.

Viking lander

Viking 1 was launched on 20 August 1975, with Viking 2 following on September 9. Viking 1 went into Mars orbit on 19 June 1976 and set its lander down on 20 July. Viking 2 went into Mars orbit on 7 August and dropped its lander on 3 September 1976.

The Viking spacecraft exceeded their planned operational lives; the Viking 2 orbiter ran out of fuel and was shut down on 25 July 1978, while the Viking 1 orbiter remained in operation until 7 August 1980. By that time, the Viking 1 lander had ceased transmissions to Earth, on 11 April 1980, but the Viking 2 lander continued to transmit until 11 November 1982.

The Viking orbiters provided a much more detailed map than that obtained from Mariner 9, returning 52,000 photographs, with the imagery including full-color shots and close-ups of selected surface features. The two landers provided panoramic landscape shots over the Martian seasons, performed chemical analysis of Martian surface materials, and obtained continuous climate data. They also provided more detailed pictures of Phobos and Deimos.

The chemical analysis system on the landers included a subsystem to detect organic molecules in Martian soil, but neither lander found any evidence of such molecules. The chemical analysis system also performed three experiments on soil samples to see if they showed evidence of metabolic processes, growth, or photosynthesis. They did reveal interesting chemical activity in some of the samples, but found nothing that suggested there really was life on Mars. Decades later, researchers speculated that the infamous dust storms of Mars might build up large static electricity charges in the soil that could produce oxidants such as hydrogen peroxide, which would explain for the anomalous chemical activity in the Viking samples. High concentrations of the corrosive oxidants would also suggest that the soil of Mars is thoroughly sterile.